Area Forecast Discussion
Issued by NWS Bismarck, ND

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688
FXUS63 KBIS 181950
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
250 PM CDT Mon Sep 18 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 220 PM CDT Mon Sep 18 2017

Quiet this evening as upper level ridging propagates across the
forecast area. Upper low and associated shortwave energy
translating through it, will impact the weather across western and
central ND late tonight through Tuesday. increasing moisture
return ahead of developing lee trough is expected to produce low
stratus advecting from Minnesota westward into the eastern and
central Dakotas. In addition strong winds aloft will spread from
western into central causing concerns for Aviation weather tonight
in the form of IFR conditions and Low level wind shear.

On Tuesday, an upper low takes shape over southern Alberta with
strong shortwave energy lifting northward through eastern MT. In
addition, a strong upper jet will track across the northern
rockies and into South Dakota. This will produce strong upper
level divergence over the eastern forecast area. The associated
surface trough/front will move from western ND Tuesday morning,
into central ND by Tuesday afternoon. This will set the stage for
potential strong to severe storms over central and eastern ND
Tuesday afternoon and evening.

Current SPC Day 2 outlook is very similar to this mornings, and
our thinking here has changed little from previous forecast.
Conditions look favorable for thunderstorm development from north
central SD into east central ND during the afternoon as strong cap
begins to erode. Timing of erosion of low stratus may affect the
eventual timing/placement of thunderstorm initiation, but the
probability of occurrence still appears high considering the
strength of the synoptic system.

NAM forecast soundings over the southern James River Valley
indicate Strong 0-6km shear congruent with 1000-1500 J/kg MLCape
and and 2-300 m2/s2 of 0-3km Helicity. This area looks to be the
most favorable for severe storms, including possible tornadic
storms, especially if initial development can remain discrete.
However, with the strength of the synoptic system, severe weather
can not be ruled out most anywhere along and east of the highway
83 corridor.

Overall few changes from the previous forecast for Tuesday.

.LONG TERM...(Tuesday night through Monday)
Issued at 220 PM CDT Mon Sep 18 2017

Severe threat will linger into Tuesday evening over the James
River Valley. As we transition into evening, threat will likely
change to more of a wind threat with linear MCS convection.

Wednesday is expected to be dry and relatively quiet. There is
some elevated instability Wednesday afternoon, so a few showers
can not be ruled out. Also it appears to be a good mixing day in
the afternoon. We bumped up winds over our given guidance,
utilizing a consensus of MOS based products.

Another upper level trough moves into the area Thursday night into
Friday. This will bring cooler temperatures with a threat of
showers. Thunderstorms can`t be completely ruled out, but higher
threat remains south and east of the forecast area.

Cooler and showery weather continues into the upcoming weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 220 PM CDT Mon Sep 18 2017

A cold front will move into western North Dakota late tonight and
into central ND by around 18 UTC Tuesday. VFR conditions today
and this evening. Low stratus may spread from southeast ND into
central portions of the state after midnight. Have introduced some
IFR-MVFR ceilings at KJMS and just a mention of an MVFR layer at
KBIS and KMOT. Will need to monitor. Brought VCSH into KDIK, KISN
and KMOT after 12 UTC. Winds begin to shift at these sites as well
12-18 UTC. More significant thunderstorm activity possible, most
likely at KJMS after the 18Z TAF period.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...TWH
LONG TERM...TWH
AVIATION...TWH



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